1. Technical Field
This invention is in the field of building construction and more particularly testing of construction elastomeric sealants and a device therefor.
2. The Prior Art
Large modern buildings are often constructed with exterior design elements (a curtain wall), such as plate glass panels or aluminum-clad window, pre-cast concrete panels, etc. The curtain wall protects from the outside weather and bears no load. The curtain wall xe2x80x9cfloatsxe2x80x9d on the superstructure of the building. On a single building one may see brick, concrete, stone and other materials, each as a horizontal ribbon interspersed with ribbons of glass. Each element is independently attached to the building and supports no other element. The exterior of the building is in effect a mosaic of different elements. Each element must have the ability to move independently of the others to allow for thermal changes, wind load and seismic movements.
These elements are connected by elastomeric sealants, which also serve to waterproof the building. The sealant is applied as a viscous liquid, which cures to a durable, flexible rubber. On most buildings that employ the curtain-wall design, the sealant becomes the only barrier between the outside and inside of the building. Although the sealant appears to be a minor part of the overall construction, it is of extraordinary importance to the performance of the building skin. Adhesion of the sealant to the elements may be adversely affected by moisture in or on the substrate during sealant application and cure, contaminated or weak surfaces, and poor application technique. Failure of the seal results in water entry, which if left unchecked, causes mold to grow. This is often the source of xe2x80x9csick building syndrome.xe2x80x9d Failure of the seal also permits air passage. It has been estimated that as much as 40% of heating and cooling costs are due to unplanned entry of air through cracks and holes in a building""s sealant.
Other uses of elastomeric joint sealants include the following. Silicone structural glazing (SSG) comprises gluing glass lites to interior mullions on the vertical jambs (two-sided SSG) and/or also on the horizontal head and sill (4-sided SSG). xe2x80x9cTilt-upxe2x80x9d style construction uses Portland Cement Concrete to create panels where the movement joints between the panels are sealed. Elastomeric movement joints are used in horizontal pavement such as in parking structures, airplane runways, bridges, etc.
A number of methods have been used to test the adequacy of elastomeric seals. ASTM C 1193xe2x80x94Standard Guide for Use of Joint Sealants describes the use of single and multi-component, cold-applied joint sealants for parallel joint sealing applications. ASTM C 920xe2x80x94Standard Specification for Elastomeric Joint Sealants covers the properties of a cured single- or multi-component cold-applied elastomeric joint for sealing, caulking or glazing operations. ASTM C 719xe2x80x94Standard Test Method for Adhesion and Cohesion of Elastomeric Joint Sealants Under Cyclic Movement (Hockman Cycle) is an accelerated laboratory procedure for evaluating the performance of a building sealant in a test configuration that is subjected to water immersion, cyclic movement and temperature change. ASTM E 330xe2x80x94Standard Test Method for Structural Performance of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference covers the determination of the performance of individual exterior elements under uniform static air pressure differences in a test chamber and is intended to represent the effects of various wind loads on exterior elements.
In the field, the current industry standard test for the functionality of sealants is a destructive test called a pull test. The pull test is performed after the sealant has cured, typically two to three weeks after application. First, a short piece of adhesive is cut from a joint by cutting from one side of the joint to the other; then starting at the first cut, two perpendicular cuts approximately 5 cm long are made along the elements. The tester grasps the freed piece of sealant firmly between the fingers and pulls away from the curtain wall at a 90xc2x0 angle or more and tries to pull the uncut sealant out of the joint. If adhesion is acceptable, the sealant itself tears (a cohesive tear) and leaves sealant attached to the substrate. Failure of the sealant to adhere to the substrate (an adhesive tear) is a test failure. Obviously, whether or not the test is successful, sealant needs to be replaced.
The current industry standard calls for one of these pull tests for every 5 levels per building elevation. For example, on a square, 100-ft by 100-ft, 20-story building, four such 2-inch tests are performed for each side of the building, or a total of 16 2-inch tests in what is perhaps a field of 8,000 linear feet of sealant. In other words, the sample is only 0.003% of the sealant. With this test if the sealant fails, usually a large area of sealant is condemned and replaced.
By way of actual example, an office building had a curtain wall of aluminum windows and architectural concrete panels with both smooth and sandblasted surfaces. The sealant stuck to the smooth concrete and metal and appeared to stick to the sandblasted areas, which was confirmed by a pull test. However, the pull test did not identify the problem of poor adherence to the sandblasted substrate because the metal side of the joint provided sufficient support to pass the pull test.
On another project, the curtain-wall elements included shop-fabricated, four-sided structurally glazed units using a two-part silicone sealant, which was also used to seal the elements. After the elements were installed and cured, a tester applied a strain to the weather seal, randomly using a blunt instrument. Adhesive failure was observed on a regular basis: approximately half of the units failed a modified ASTM E 330 test. Remediation of all sealant was very costly and included removal of all the weather seals, installation of temporary fastening clips, cleaning out the double-sided tape, pumping the structural sealant into the joint, allowing it to cure and finally reinstalling the weather seal. If an efficient non-destructive test had been available, faulty units could have been identified in the shop and only half of the sealant on the building would have required repair.
There is currently no industry standard test method that can provide on-site information as to the adequacy of the sealant without destroying existing joints.
A device for determining the adequacy of a sealant between construction elements is attached to a source of compressed air whose pressure is controlled by a regulator. The device includes a cylinder containing at least one piston, the piston containing an air chamber and a plunger, the air chamber being in communication with a pressure gauge. The device also includes an armature having a first and a second end, the first end being attached to the cylinder, the second end having a flow valve and an air fitting in communication with the air source, the handle containing tubing as a means to conduct air from the compressed air source, the tubing being interrupted with a bleed valve. The device also includes a moveable tip such that the tip moves in the direction parallel to the axis of the cylinder, said tip comprising a wheel, a wheel bracket and a plunger shaft, the plunger shaft being attached to the plunger within the piston; In use, the operator holds the device so that the moveable tip presses against the sealant with constant pressure.
In another embodiment, the moveable tip is removable. In yet another embodiment, the pressure gauge is visible when the device is in operation. In yet another embodiment, the handle contains two bleed valves.
In yet another embodiment, there is provided a method of field testing the adequacy of sealant between two adjacent materials which are the same or different. The method includes providing a bead of sealant between two materials; permitting the sealant to cure; providing a device which is capable of exerting a constant pressure on the sealant and for which the pressure can be adjusted; applying the device to the bead at a variety of pressures to establish an optimal pressure to test the sealant in the field; applying the device with the optimal pressure to the sealant in the field; and observing for any separation of the sealant from the materials and any indentation of the sealant.